A Neurobiological Approach to Understanding Human Intelligence

Is human intelligence measurable? … quantifiable? Perhaps, you came across this popular catchphrase purportedly quoted by the genius, Albert Einstein: “Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.” One of the most popular methods of measuring intelligence is by intelligence quotient (IQ) tests. The accuracy of the results is highly debatable though. These tests have long been criticized for being not all-inclusive, and therefore may not fully represent human intelligence.

Human intelligence – how the brain works

The brain is one of the most studied parts of the human body and yet scientists are still mystified as to how it completely works and how it hallmarks the uniqueness of human intelligence. An adult human brain is comprised of neurons and glial cells. While the glial cells are primarily for support, the neurons are essential for cell-to-cell communication, particularly for conducting nerve impulses. The neurons are excitable cells with specialized parts (e.g. soma, dendrites and axons), structures (e.g. synapses), and chemicals (e.g. neurotransmitters). In essence, the neuron generates nerve impulses that travel along the axon, resulting in the release of neurotransmitters that bind to the receptors of the dendrites of the target neuron. The ensuing effect may either be excitatory or inhibitory. The integration of these nerve impulses leads to the brain carrying out higher brain functions, such as language, speech, emotions, memory, learning, etc. The brain is truly a spectacular organ in charge of a mélange of tasks epitomizing human intelligence.

An illustration of the process of synaptic transmission in neurons

Human intelligence measured by IQ tests

IQ tests were devised to measure human intelligence based on the ability of an individual to generate answers that rely on reasoning and information, and how quickly. They are used in order to figure out if a person is capable of making quick, knowledgeable, and logical answers, especially in situations requiring immediate solutions. In educational settings, IQ tests help teachers predict which areas a student excels at and which ones a student would need extra help. However, making speculative conclusions based on IQ test results may lead to bias and wrong assumptions. For instance, predicting future success based on IQ or even on human intelligence is not as simple as it seems. It takes perseverance, passion, and sometimes, even luck. What a high IQ could point at is the person’s aptitude for certain realms of human intelligence.

Measures of human intelligence by neurobiological means

3D illustration of the human brain. (Credit: yodiyim)

Apart from IQ test-based measures, other methods have been designed to perceive and measure human intelligence. One of which is the integration of neurobiology. Researchers began to look at the structure of the brain and how it functions. Aki Nikolaidis, a neuroscientist, conducted a study with colleagues. Fluid intelligence was monitored through magnetic resonance spectroscopy on adult volunteers while taking IQ tests. Fluid intelligence is a form of intelligence primarily based not on stored knowledge but on the ability of a person to solve complex problems without prior information. In their study, they identified the specific parts of the brain that were active during fluid intelligence. They found that the predictor of fluid intelligence is located on the left frontal and parietal parts of the brain, independent of the brain size.1 Another recent study suggests that intelligence is inversely proportional to the number of dendrites the individual has. Accordingly, smarter people tend to have fewer brain dendrites, which implies that they have fewer connections between neurons in their cerebral cortex. In other words, the more intelligent a person is, the fewer brain wirings he or she needs for a brain function.2

How the brain works and how it is structured are just a few of the facets that researchers tap to understand human intelligence. Future research insights are crucial in order to methodically define what human intelligence is, and find ways, if not to boost it, keep it fairly functional even in the declining years.